The cochlear nucleus (CN) is the first location in the brain where acoustic information from the cochlea is received via the cochlear nerve, processed, and transmitted to other auditory nuclei. The synaptic arrangements in the normal CN must play a key role in processing acoustic messages and, thus, in how these messages are interpreted by the rest of the brain. To understand the synaptic and cellular basis of information processing in the normal CN, it is necessary to define the influence of cochlear, centrifugal, and local inputs on each type of neuron in the CN. As one step toward that goal, the studies proposed here attempt to identify the neurons making synaptic contacts in the CN that use excitatory and inhibitory amino acid transmitters, and to identify some of their synaptic contacts and targets in the CN. Neurochemical studies will focus on the CN and determine if the synaptic endings of particular groups of neurons store, release, and inactivate (by high-affinity uptake) amino acid transmitter candidates. In histochemical studies, light and electron microscopic autoradiographic analyses will be used to verify the uptake sites in the CN. Transmitter-specific retrograde radiolabeling of neurons, visualized with light and electron microscope autoradiography, will be used to identify neurons projecting to, and within, the CN that could use a particular amino acid transmitter candidate. Immunohistochemical methods will be used to identify neurons containing gamma-aminobutyric acid and glutamate decarboxylase which could use gamma-aminobutyric acid as a transmitter in the CN. The histochemical studies should enable us to identify the synapses and targets of several types of neurons that use an amino acid transmitter.